After bebe3d626e, b->fail_jump is prepared after vtn_create_builder
which can longjmp(3) to it through its vtx_assert()s. This corrupts
the stack and creates confusing core dumps, so we need to avoid it.
While there, I decided to print the offending values for debugability.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Martin Pelikán
53719f818c